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  A person eats a substance or allergen that causes an allergic reaction.
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  When the individual eats the substance, the body creates an antibody, or a protein that detects harmful substances.
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  This antibody, attatches itself to cells found in tissues all over the body in order to prepare the body for if that allergen enters the body again.
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  When the food allergen enters the body again, the allergen binds to the antibodies and sends out signals to the body to release large amounts of histamine.
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  The histamine causes irritation and swelling in parts of the body.
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  The result of this irritation varies in person to person, from mild hives, shortness of breath, to anaphylaxis.